1. Technical Field of the Invention
The invention present relates to sunscreen compositions comprising, formulated into a cosmetically acceptable carrier, at least one system for screening out UV radiation, and containing:
(a) at least metal oxide mineral pigment, and
(b) at least one specific hydroxyalkylurea compound.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation with wavelength of from 280 nm to 400 nm permits tanning of the human epidermis and that rays with wavelengths of from 280 to 320 nm, which are known as UV-B rays, cause skin burns and erythema that can harm the development of a natural tan; this UV-B radiation should therefore be screened out.
It is also known that UV-A rays, with wavelengths of from 320 to 400 nm, which cause tanning of the skin, are liable to induce an impairment in the skin, especially in the case of sensitive skin or skin that is continually exposed to solar radiation. UV-A rays in particular bring about a loss of elasticity of the skin and the appearance of wrinkles, leading to premature aging. They promote the triggering of the erythemal reaction or amplify this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. It is therefore desirable also to screen out UV-A radiation.
UV-A and UV-B rays should therefore be screened out, and cosmetic compositions for protecting the human epidermis containing UV-A- and UV-B-screening agents currently exist.
The UV-screening agents most commonly used are organic and soluble in oils or in aqueous media; they generally have, within their structure, a chromophore group linked to a solubilizing group, which is generally a fatty chain in the case of liposoluble UV-screening agents or else a carboxylic or sulfonic acid group in the case of water-soluble UV-screening agents.
Many cosmetic compositions intended for photoprotection of the skin have been proposed to date, and the use of metal oxide nanopigments, such as TiO2 nanopigments, in anti-sun products is increasingly common since they make it possible to obtain very high protection indices in combination with conventional UV-screening agents.
The anti-sun compositions are quite often in the form of an emulsion, of oil-in-water type (i.e., a cosmetically and/or dermatologically acceptable carrier consisting of a continuous aqueous dispersing phase and of a discontinuous fatty dispersed phase), or of water-in-oil type (aqueous phase dispersed in a continuous fatty phase), which contains, in varying concentrations, one or more conventional lipophilic organic screening agents and/or conventional hydrophilic organic screening agents capable of selectively absorbing the harmful UV radiation, these screening agents (and the amounts thereof being selected as a function of the desired sun protection factor, the sun protection factor (SPF) being expressed mathematically as the ratio of the dose of UV radiation required to reach the erythema-forming threshold with the UV-screening agent to the dose of the UV radiation required to reach the erythema-forming threshold without the UV-screening agent. In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase.
One of the major drawbacks of the anti-sun compositions known to date that contain metal oxide, in particular titanium oxide, mineral pigments is that, once applied to the skin in the form of a film, they engender, on the latter, a whitening effect that is cosmetically undesirable and in general not very well liked by users. The higher the concentration of pigments in the composition, the more marked this effect is. In order to prevent this problem, it would, of course, be possible to use reduced amounts of pigments, but the resulting emulsions, which would admittedly result in an acceptable transparency on the skin, would then no longer offer suitable protection in the UV range, which greatly limits the advantage of such an operation.
Another difficulty lies in the fact that conventional anti-sun emulsions based on protective pigments produce, after application to the skin, an uneven, nonhomogeneous, or even coarse, distribution of the pigments on this skin, which may be harmful to the quality of the overall photoprotective effect. This poor pigment distribution that is observed at the surface of the skin is often linked to the fact that, in terms of the initial composition itself (before application), there is a substantial lack of homogeneity (poor dispersion of the pigment in its carrier).
The inclusion of titanium oxide pigments (Tioveil AQ) in a depigmenting lotion containing kojic dipalmitate has already been proposed. This formulation does not make it possible to remedy the technical problems mentioned above.